Rich black is a CMYK mix. No registration is absolutely perfect; there is always a little shift or stretch. Make sure that all black text is set at 100% black. This means the text is only printed once with the black plate, eliminating registration problems.
Solid black areas of colour
With digital printing you don’t need as much ink to achieve a good black solid. In fact if you use too much ink your print will suffer in quality. If you want a rich black solid, use these values:
This gives you an overall ink coverage of 190%